Tau (particle)

Not to be confused with the τ+ particle of the τ–θ puzzle, which is now identified as a kaon.

Tau
CompositionElementary particle
StatisticsFermionic
FamilyLepton
GenerationThird
InteractionsGravity, electromagnetic, weak
Symbol
τ−
AntiparticleAntitau (
τ+
)
DiscoveredMartin Lewis Perl et al. (1975)[1][2]
Mass3.16754(21)×10−27 kg‍[3]
1776.86(12) MeV/c2[4][5]
Mean lifetime2.903(5)×10−13 s[5]
Electric charge−1 e[5]
Color chargeNone
Spin⁠1/2⁠ ħ[5]
Weak isospinLH: −⁠1/2⁠, RH: 0
Weak hyperchargeLH: −1, RH: −2

The tau (τ), also called the tau lepton, tau particle, tauon or tau electron, is an elementary particle similar to the electron, with negative electric charge and a spin of ⁠1/2⁠. Like the electron, the muon, and the three neutrinos, the tau is a lepton, and like all elementary particles with half-integer spin, the tau has a corresponding antiparticle of opposite charge but equal mass and spin. In the tau's case, this is the "antitau" (also called the positive tau). Tau particles are denoted by the symbol
τ−
 and the antitaus by 
τ+
.

Tau leptons have a lifetime of 2.9×10−13 s and a mass of 1776.9 MeV/c2 (compared to 105.66 MeV/c2 for muons and 0.511 MeV/c2 for electrons). Since their interactions are very similar to those of the electron, a tau can be thought of as a much heavier version of the electron. Because of their greater mass, tau particles do not emit as much bremsstrahlung (braking radiation) as electrons; consequently they are potentially much more highly penetrating than electrons.

Because of its short lifetime, the range of the tau is mainly set by its decay length, which is too small for bremsstrahlung to be noticeable. Its penetrating power appears only at ultra-high velocity and energy (above petaelectronvolt energies), when time dilation extends its otherwise very short path-length.[6]

As with the case of the other charged leptons, the tau has an associated tau neutrino, denoted by 
ν
τ.

  1. ^ Cite error: The named reference Perl1975 was invoked but never defined (see the help page).
  2. ^ Okun, L.B. (1980). Leptons and Quarks. Translated by Kisin, V.I. North-Holland Publishing. p. 103. ISBN 978-0444869241.
  3. ^ "2022 CODATA Value: tau mass". The NIST Reference on Constants, Units, and Uncertainty. NIST. May 2024. Retrieved 18 May 2024.
  4. ^ "2022 CODATA Value: tau energy equivalent". The NIST Reference on Constants, Units, and Uncertainty. NIST. May 2024. Retrieved 18 May 2024.
  5. ^ a b c d Tanabashi, M.; et al. (Particle Data Group) (2018). "Review of Particle Physics". Physical Review D. 98 (3): 030001. Bibcode:2018PhRvD..98c0001T. doi:10.1103/PhysRevD.98.030001. hdl:10044/1/68623.
  6. ^ Fargion, D.; de Sanctis Lucentini, P.G.; de Santis, M.; Grossi, M. (2004). "Tau air showers from Earth". The Astrophysical Journal. 613 (2): 1285–1301. arXiv:hep-ph/0305128. Bibcode:2004ApJ...613.1285F. doi:10.1086/423124. S2CID 119379401.